Carbon nanotubes are very small tube-shaped structures essentially having the composition of a graphite sheet, formed as a tube. Carbon nanotubes produced by arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes have very good electrical conductance due to their structure. They are also chemically stable, and have very small diameters (less than 100 nanometers) and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that carbon nanotubes can play an important role in fields such as microscopic electronics, materials science, biology and chemistry.
Although carbon nanotubes promise to have a wide range of applications, better control is needed over the building and organization of nanotube-based architectures. Normally, the orientation of growing nanotubes is controlled such that the nanotubes are rectilinear and parallel to each other. Chemical vapor deposition has been used to produce nanotubes vertically aligned on catalyst-printed substrates.
There have been reports of growth of aligned carbon nanotubes using chemical vapor deposition, for instance, Z. F. Ren et al. entitled “Synthesis of large arrays of well-aligned carbon nanotubes on glass” (Science, Vol. 282, Nov. 6, 1998, pp. 1105-1107), S. S. Fan et al. entitled “Self-oriented regular arrays of carbon nanotubes and their field emission properties” (Science, Vol. 283, Jan. 22, 1999, pp. 512-514), B. Q. Wei et al. entitled “Organized assembly of carbon nanotubes” (Nature, Vol. 416, Apr. 4, 2002, pp. 495-496), Yoon-Taek Jang et al. entitled “Lateral growth of aligned mutilwalled carbon nanotubes under electric field” (Solid State Communications, Vol. 126, 2003, pp. 305-308), and Ki-Hong Lee et al. entitled “Control of growth orientation for carbon nanotubes” (Appl. Phys. Lett., Vol. 82, Jan. 20, 2003, pp. 448-450).
However, carbon nanotubes obtained by the above-mentioned methods are aligned along a linear direction, and/or extend perpendicularly from the substrates. Furthermore, the method of using an external field such as an electric field or a magnetic field, to control a direction of growth of the carbon nanotubes is difficult to apply in generating localized complicated structures with plural orientations of the carbon nanotubes. Accordingly, the range of diversity of different kinds of carbon nanotube-based devices is limited.
What is needed is to provide a method for making a carbon nanotube-based device with plural orientations of carbon nanotubes.